MELBOURNE (Reuters) - Renault said they have fixed their pre-season power unit problems with a "belt and braces" approach ahead of Formula One's Australian Grand Prix opener.

Issues with the unit's Energy Recovery System (ERS) limited the team's mileage in the second Barcelona test this month, although the car was clearly a significant step up on last year's.

"We have addressed the ERS issue which caused us reliability concerns and do not expect to see a repeat of it in Australia," Renault Sport F1 managing director Cyril Abiteboul said in a team preview for Sunday's race in Melbourne.

"We know we have a strong base with the RS17 (car) which puts us in good stead for the relentless development race we expect to see," he added.

Technical head Bob Bell said he was "reasonably confident" after testing.

"Even though we did experience some issues we don't have any overriding concerns over reliability as we accumulated sufficient data and have taken remedial and precautionary measures to address the particular ERS issue we saw," he said.

Bell said the ERS issue had been seen previously in static dyno tests at the factory "but packaged in the car and out on track it was amplified.

"Since Barcelona we've adopted a belt and braces approach to avoid a similar issue in Melbourne," he added.

Renault have a changed lineup this season, with Germany's Nico Hulkenberg coming in from Force India to partner Britain's Jolyon Palmer, and an all-new power unit that they hope will help close the gap to Mercedes.

The former champions finished ninth last year, their return as a constructor after taking over the failing Lotus team at the end of 2015, but have set their sights on fifth in 2017.

Hulkenberg expected Renault to be among the midfield teams in Australia but improving steadily.